The invention relates to a power output stage, in particular for a controller of an electrical machine for a motor vehicle, comprising at least one control unit and comprising at least four semiconductor switches which can be individually actuated by the control unit and which are connected to at least two half-bridges for operating the electrical machine in order to form a bridge circuit, and are connected to a supply line and an earth line of the power output stage.
The invention further relates to a method for operating such a power output stage.
Power output stages as well as a method for operating the same are known from the technical field. In order to drive electrical machines, so-called clocked output stages or power output stages are frequently used which actuate the electrical machine by means of semiconductor switches that are interconnected in a bridge circuit. A constant supply d. c. voltage can be converted into a variable operating d. c. voltage for the electrical machine by means of a clocked, individual actuation of the semiconductor switches. So-called MOSFET switches are frequently used as semiconductor switches in this context. In order to protect the electrical machine as well as the power output stage from damage, a short-circuit detection is as a rule implemented into the power output stage in terms of device and/or process technology. The short-circuit detection in discrete MOSFET switches generally takes place by means of a drain-source voltage measurement in the control unit which actuates the semiconductor switches. In so doing, a high-voltage side semiconductor switch of a first bridge and a low voltage side semi-conductor switch of a second bridge are, for example, switched on and the voltage drop across the respective semiconductor switch is detected and compared to a target value. If the detected voltage does not lie in the expected range, the control unit can accordingly react and, for example, deactivate the power output stage. The disadvantage thereby is that this form of short-circuit detection can only be carried out in a power output stage through which current is passed. In addition, the drain-source voltage depends heavily on the on-state resistance of the respective semiconductor switch as well as on the short-circuit current. The first publication of the Japanese patent application JP 2005 067 380 A furthermore discloses a device and a method which enable a short-circuit detection of a bridge circuit which is designed as an H bridge without the electrical machine having to be driven.